SGER: A Multi-Gene Approach to Understanding Relationships Among Ciliates in the Class Spirotrichea

Smith College, Northampton MA

Investigators

Abstract

DEB-0079325 Laura A. Katz Dr. Laura A. Katz has been awarded a grant to study the evolution of a fascinating type of microorganisms known as ciliates, a diverse group of protozoa characterized by the presence of two types of nuclei in each cell and by unusual molecular processing of their chromosomes. Unlike many plants and animals, we currently have only a basic framework for interpreting the evolutionary history of these organisms. For example, in the past twenty years, as techniques for identifying species have improved, the number of classes of ciliates has risen from only three based on microscopic analyses, to eight based on electron microscopy, to at least nine based on DNA sequence data. The class Spirotrichea represents a particularly contentious assemblage of ciliates as previous analyses provide varying pictures of which ciliates belong within this class and how these ciliates are related. Ciliates thought to belong to the class Spirotrichea can be found in both freshwater and marine ecosystems, and are characterized by diverse, and sometimes dramatic, arrangements of their ciliature. Our current classification system is based on limited data from only a handful of taxa. Analysis of multiple genes from a comprehensive survey of ciliates is needed to accurately reconstruction relationships among these organisms. The overall goals of this study are (1) to identify species of ciliates that belong to the class Spirotrichea, and (2) to reconstruct relationships among these species. To achieve these goals, DNA sequences will be determined for three genes (small subunit rRNA, alpha-tubulin and the largest subunit of the DNA polymerase II) from potential members of the class Spirotrichea. In addition, sequences will be characterized from appropriate outgroup species (non-spirotrichs). The resulting DNA sequences will be aligned using at least two alignment methods and estimates of species relationships will be made using several phylogenetic methods (e.g. maximum parsimony and maximum likelihood) on both individual genes and a combined data set. The resulting genealogies will answer questions about the evolutionary history of spirotrichs, while also indicating areas for future research on the relationships among ciliates.